As a semiconductor device which can suppress short-channel characteristics and suppress element variations, a semiconductor device using a SOI substrate is used in these days. The SOI substrate is a substrate obtained by forming a BOX (Buried Oxide) film (embedded oxide film) on a supporting substrate made of high-resistance Si (silicon) or others, and forming a thin layer (silicon layer, SOI layer) mainly containing Si (silicon) on the BOX film. If a MOSFET (Metal Oxide Semiconductor Field Effect Transistor: MOS-type field effect transistor) is formed on the SOI substrate, the short-channel characteristics can be suppressed without introducing an impurity into a channel layer. As a result, mobility can be improved, and element variations due to impurity fluctuation can be improved. Therefore, by manufacturing a semiconductor device using the SOI substrate, improvement in the integration density and operating speed of the semiconductor device and improvement in an operating margin caused by reduction in variations can be expected.
Patent Document 1 (Japanese Patent Application Laid-Open Publication No. 2004-146550) describes that a gate electrode of an N-channel-type MOSFET on a SOI substrate is made of a P-type semiconductor film. There is no description about a P-channel-type MOSFET therein, and the document describes that the film thickness of the gate electrode is about 200 nm.